Agritechnica 2016

Soil Compaction in GrasslandJohn Maher

Teagasc, Ireland

600 mm

3000 mm

1300 mm

Monthly Rainfall (mm) in Ireland

Conservation

Grazing

• 285 Days of Feed• Cost of feed (Energy Basis)

– 33% Cost of Grass Silage– 25% Cost of Concentrate

• Grazed Grass: High Feed Value– Provided it is managed well

• Cows Feed themselves– Avoids harvesting cost– Avoids storage cost & Feeding out cost

• Cows Spread their own Slurry

Why Grazed Grass???

Soil TypeCompact Easily

Sand 6%

Silt 53%

Clay 41%

Less Compaction

Sand: 46%

Silt: 46%

Clay 8%

Compaction Causes

Animal Traffic Machinery Traffic

Soil Structure + Compaction

StructureArrangement of soil particles and pore spaces

between them

Critical to all soil functions

CompactionAlteration of the soil structure by compressive

forces

Threats to structure

Increased machine weight

Increased intensity of operations

Extended grazing season

Compaction effectsDirectly impedes root growth

• Influences access to nutrients and water

Reduces soil pore space (50% - 30%)• Less aeration for biological function

• (impacts on nutrient cycling: Denitrification)

• Less inflitration / drainage:• Further root growth restriction

Reduced uptake of nutrients (water)Reduced plant growth

Practical Impacts

Reduced yield (grass or crop). Inefficient use of nutrients Ponding/Water on surface Weed grasses etc. Delayed field operations Machine Grazing

Compaction + Yield

Yield Reductions Cereals 0 to 20% Maize 0 to 50% Grass 8 to 30%

Teagasc Research:

Compaction Risk Factors Soil type (including OM) Presence or absence of

vegetation Soil Moisture Content Machine weight, Ground pressure Traffic density Animal weight + Traffic density

Depth + DurationShallow (<150 – 200mm)

• Frequent in arable – cultivation resolves?

• Frequency in GrasslandDeep (>200mm)

• More difficult to resolve in all soilsPersistence of compaction

• Typically 2 to 7 years• Can be longer

Compacted Top-Soil Compacted Sub-Soil

Soil Examination (Visual)Spade – extract 300mm undisturbed profileExamine for:

• Blocky, platy structure vs Crumb structure• Horizontal layering vs vertical channels,

‘Pans’• Earthworms• Grey mottling • Deep invasive roots

Examine Profile

300mm Spade-full

Preventing Compaction

Land Drainage (Deep Drains 1.8m)

Land Drainage (Shallow Drains 0.8m)

How do we ‘Prevent’?Restrict TrafficAnimals: Grazing management Field Infrastructure Housing (get animals off when necessary) Breeding for Smaller CowsMachinery:

Avoid in wet conditionsReduced loads and PressuresLarger tyres/Lower Pressure

Tomorrow

Morning

Evening

Tomorrow

Evening

Morning

Day 1 am

Day 1 pm

Day 2 am

Day 2 pm

Day 1 am

Day 1 pm

Day 2 am

Cow Walk Spokes of Wheel Strip-grazing

Roadway Farmyard

Grazing from Back

Entry EXIT

GRAZING TECHNIQUES:

2.0 bar GP

4t8t

1.0 bar GP 2.0 bar GP

Weight

Tyres

ContactArea

4t

Air in tyre supports load

Inflation pressure = Ground pressure

Large tyres - big volume - low pressure

0.5m

1.0m

100kpa

75kpa

50kpa25kpa

1.0 bar GP 1.0 bar GP

2t 4t

Soil Level

Axle load is important

“Fixing” Compaction

Option 1: TimeAllow soils to self repair

• Shrinking + swelling can help• Frosts? (shallow)• Must remove compaction cause (if obvious)

Inexpensive and avoids doing harmMay not be adequate !

Grassland - AerationShallow loosening (100 - 200mm) – “Spiker”

Teagasc Research• 10 trial sites 3 years, multiple harvests.

• Some Initial responses (maybe N Mineralisation)

• No response to routine treatment

Subsoiling / Deep LooseningLoosens by shattering

• to greater depth 300-400mm

Power demanding (45 kW / leg at 400mm)Leg spacing depends on depth and wings

• With wings = 2 x depth• E.g. At 300mm depth: 600mm spacing: 5 legs in 3m

Grassland• Not suitable for rock / stone

Deep Loosening Effective?Prevention is better than cure

• Avoid the need for deep loosening

Research not clear-cut• Some Negative results• Some Slightly positive results• Little Longterm Benefit• Arable research

• Re-compaction risk is real

Re-compaction riskLoosened soils

• Loose to depth of subsoiler • More moisture through profile

Prone to Re-Compaction

• May compact to deeper depth • Shifting problem down

• even more difficult to solve

Soil Compaction

Prevention is Betterthan Cure!!!

Prevention is better than Cure